Most of the OE Brembos won't work on the ST. Gotta do the math, piston area has to be pretty close or pedal will go to the floor. Handicap on the ST is we're starting with a single piston, any 4 pot swap has to have very small pistons to work. Looked into this a bit myself with calipers readily sourced in US, easy part is 300mm Focus SVT front calipers rotors are bolt-on. Other things to consider are orientation (can't swap sides with calipers) and hose connection. I've pretty much decided easiest/cheapest route would be to just fab spacers for factory front calipers, no Brembo bling but greater thermal mass and diameter and perfect match for SVT rears.